The present invention relates to capping machines for affixing plastic screw closures on glass or plastic containers for beverages or the like. More particularly it relates to the head portions of a capping machine which serve to rotate the plastic screw cap with respect to the container while pressing on the cap and applying a limited predetermined tightening torque to the cap as controlled by an internal slip clutch.
The development of capping machine heads has been impelled in considerable part by the changes in closures which have progressed from the traditional crowns, to roll on aluminum caps, then to plastic screw caps. With the advent of plastic screw caps with peripheral serrations, it became important to provide the capping machine heads with a slip clutch or other means so that the rotation of the upper part of the head with the spindle after the screw cap was tightly seated would not impart excessive torque causing the cap to be over-tightened or broken. Such caps usually have serrations or teeth positively engaged by matching teeth of the cap chuck. Although some such clutches were friction slip clutches, in recent years, magnetic clutches or magnetic drives-frequently have been employed to control the torque applied to the screw caps.
Numerous patents showing related subject matter in the field of capping machine heads is cited in the current application Ser. No. 07/787,011, but these patents generally show a form of chuck and cap receiver in which the sides of the receiver are tapered not only at the opening end but throughout the depth of the cap receiver. Furthermore, those related patents generally do not show a cap receiver having a relatively wide shoulder which acts as a stop and abutment for the top of the screw cap to assure its coaxial alignment. U.S. Pat. No. 4,558,554 to James F. Herbert, issued Dec. 17, 1985 (Cl.53/331.5) shows a capping head with a cap receiver 27 having a somewhat-tapered internally serrated member 30. The collet (projection) of Herbert has a shoulder (not numbered) but such shoulder is generally occluded by the serrated member 30 and does not appear to function as a stop for the screw cap.
In the apparatus of the invention a conventional plastic cap with a serrated peripheral surface is positively gripped by the receiver of the chuck portion having a relatively shallow toothed section spaced from an intrusion limiting shoulder; the receiver cylinder in the vicinity of, the toothed section has little or no taper.